Heretofore, floating cranes have been provided for building bridges, loading and unloading from docks, etc. which have typically included a rectangular barge structure upon which a crane is carried. Such rectangular barges typically range up to 200 ft. in length and 50 ft. in width, accommodating booms up to 300 ft. in length. When the crane boom carried on the barge swings laterally, the end of the barge loaded by the boom dips into the water placing side loads on the boom which, under certain severe conditions, can cause collapse of the boom. The resulting tilting of the barge to one side as the boom swings, makes accurate positioning of the boom difficult and makes the whole structure out of level. Waves from natural causes or from passing ships or even a small yacht can cause considerable lift and side loading of the boom structure.
Boom lengths have been limited on rectangular barges since the problems of maintaining the floating apparatus level and boom side loading increases with the length of the boom.
In my co-pending application entitled FLOATING CRANE APPARATUS, filed on Sept. 4, 1979, Ser. No. 06/072,347, there is disclosed a floating crane apparatus which includes a generally annular float assembly comprising individual pontoon members. Frame means interconnect a number of the pontoon members and are pivotally carried by a bridge so they can be pivoted inwardly when the pontoon members are disconnected for transportation.
A boom is operatively carried by the bridge and the float assembly for movement in a generally vertical plane. Propulsion means is carried by the float assembly for rotating the float assembly thereby moving the hoist boom means laterally in a unitary manner.
As disclosed in my co-pending application, a spud anchor is centrally located relative to the float assembly so that the entire floating crane can be rotated around the vertically extending spud anchor during operation.
One problem in utilizing a spud anchor is that its operation is limited by the depth of the water in which the crane is being operated.
Another problem of rotating the floating crane about a fixed spud is that if the crane is being utilized to unload a ship that is anchored, and the ship shifts due to current, it would tend to run over the floating crane tending to damage the crane and the spud that is anchored in the bottom.